PVC Conduit Thermal Expansion (NEC 352.44)
Length change of a PVC raceway over its temperature swing, against the NEC trigger.
Example
You enter
- Straight run between anchors (ft) 100
- Temperature swing (°F) 50
- PVC coefficient (in/in/deg-F) 0.0000338
- Fitting trigger (in) 0.25
You get
- Length change 2.028 in
Details, formula, and sources
The longitudinal length change of a PVC raceway across its temperature swing (delta_L = coefficient x length x temperature change) against the NEC 352.44 quarter-inch expansion-fitting trigger, for outdoor or unconditioned runs. The AHJ and the conduit manufacturer govern.
delta_L = coefficient x (run_length_ft x 12) x temperature_change; an expansion fitting is required once delta_L reaches the 1/4-inch (0.25 in) trigger, sized for that travel. PVC coefficient 3.38e-5 in/in/deg-F.
NEC 2023 (NFPA 70). 352.44 (expansion fittings for rigid PVC conduit).
Free read-only access at nfpa.org/freeaccess.
Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
Field names used by the API: run_length_ft, temp_change_f, coeff_in_per_in_f, trigger_in, delta_l_in
- PVC coefficient the bundled 3.38e-5 in/in/deg-F coefficient is the public PVC physical property underlying NEC Table 352.44; the manufacturer's published coefficient governsNEC 2023 Table 352.44 / PVC manufacturer
- Temperature swing the temperature change is the maximum-minus-minimum the conduit will see; a zero or negative swing yields zero expansion to absorbsite temperature extremes; the AHJ governs